NPZ Models of Plankton Dynamics: Their Construction, Coupling to Physics, and Application

Nutrient-phytoplankton-zooplankton (NPZ) models have been in use in oceanography for at least three decades, and are still a common research tool. Given the discoveries of the last two decades, particularly concerning the role of bacteria in the plankton, there are questions as to whether NPZ models can still be supported as a useful tool in planktonic research. Here I review the construction of NPZ models, and some of the physical platforms they have been coupled to. I then discuss the applications of NPZ-physical models, and conclude that they still constitute an important and viable research tool, provided that the questions being explored are clearly stated. This revised version was published online in August 2006 with corrections to the Cover Date.     

The acid neutralizing capacity （ANC） of South Africa＇s freshwater ecosystems

Acidification is considered the most important one of the primary chemical stress factors that impact on freshwater ecosystems. In unpolluted freshwater systems, the primary controls on the degree of acidification are factors such as the geological substrate of the catchment area, the presence of organic acids secreted by vegetation in the river system, and equilibrium exchange of carbon dioxide with the atmosphere. Anthropogenic factors that can impact on the degree of acidification of freshwater systems include agricultural, mining and industrial activities, either through direct runoff into river systems or through deposition of atmospheric pollutants from these sources. The capacity factors alkalinity and acidity, which represent the acid- and base-neutralizing capacity （ANC and BCN） of an aqueous system, have been used as more reliable measures of the acidic character of freshwater systems than pH. Unlike pH, ANC and BNC are not affected by parameters such as temperature and pressure. Therefore, ANC has been employed as a predictor of biological status in critical load assessments. Freshwater systems with ANC＇s eq/L isμeq/L are considered sensitive to acidification, ANC=0 μbelow 150 commonly used as the predictor for fish species such as trout in lakes, and an eq/L as more realistic for streams. Acid-neutralizing capacity μANC value of 40 （ANC） can be determined by titration with a strong acid to a preselected equivalence point. Alternatively, it can be calculated as the difference between base cations （[BC]） and strong acid anions （[SAA]）： ANC=[BC]- [SAA]=[Ca^2＋]＋[Mg^2＋]＋[Na^＋]＋[K^＋]-[SO4^2-]-[NO3^-]-[Cl^-] To date, there has been no attempt to establish the ANC of South Africa＇s freshwater ecosystems or variability therein, despite the fact that long-term water quality monitoring data exist for all the parameters needed to calculate it according to the above equations. As a result, the relationship between the acid neutralizing capacity of freshwater ecosystems in South Africa and biodiversity factors, such as fish status, is unknown. Results of the first comprehensive （country-wide scale） evaluation of the acid neutralizing capacity of river systems in South Africa will be presented. Long-term monitoring data obtained from the Department of Water Affairs and Forestry （DWAF） from most of South Africa＇s river systems were used to establish geographic and temporal variabilities in ANC. The results show that the Berg and Breede River systems are most susceptible to acidification, and that geological substrate appears to explain most of the geographic variabilities observed.     

Establishment of apparent quantum yield and maximum ecosystem assimilation on Tibetan Plateau alpine meadow ecosystem

The alpine meadow is widely distributed on the Tibetan Plateau with an area of about 1.2×106kn2. Damxung County, located in the hinterland of the Tibetan Plateau, is the place covered with this typical vegetation. An open-path eddy covariance system was set up in Damxung rangeland station to measure the carbon flux of alpine meadow from July to October,2003. The continuous carbon flux data were used to analyze the relationship between net ecosystem carbon dioxide exchange (NEE) and photosynthetically active radiation (PAR), as well as the seasonal patterns of apparent quantum yield (α) and maximum ecosystem assimilation (Pmax).Results showed that the daytime NEE fitted fairly well with the PAR in a rectangular hyperbola function, with α declining in the order of peak growth period (0.0244 μmolCO2 · μmol-1pAR) ＞early growth period ＞ seed maturing period ＞ withering period (0.0098 μmolCO2 · μmol-1pAR).The Pmax did not change greatly during the first three periods, with an average of 0.433mgCO2· m-2· s-1, i.e. 9.829 μmolCO2· m-2· s-1. However, during the withering period, Pmax was only 0.35 mgCO2 · m-2 · s-1, i.e. 7.945 μmolCO2 · m-2 · s-1. Compared with other grassland ecosystems, the α of the Tibetan Plateau alpine meadow ecosystem was much lower.     

我国典型资源枯竭型城市生态系统健康综合评价

资源枯竭和环境恶化影响着典型资源枯竭型城市的发展。根据"压力-状态-响应"模型,构建了一个度量典型资源枯竭型城市生态系统健康水平的含有4个层次35项具体指标的指标体系,并运用客观的改进的熵值法赋权、模糊综合评价法及划分的等级标准对我国9个典型资源枯竭型城市的生态系统健康水平进行量化分析。结果表明,阜新市的生态系统健康水平属于"较健康"级,伊春、辽源、白银、焦作属于"临界状态"级,盘锦、白山、萍乡属于"较不健康"级,而石嘴山则属于"不健康"级。典型资源枯竭型城市的生态系统健康水平总体上不容乐观。     

不同土地利用方式下的七里海湿地临界评价研究

在"湿地临界"概念的基础上,定性分析了湿地利用与保护的平衡状态,探讨了不同利用方式下的湿地临界的研究步骤,并从基于耕地和河蟹养殖地两种土地利用方式入手,对七里海湿地临界进行了评价。研究表明,通过建立湿地临界模型,从经济效益评价和生态效益的评估入手,对湿地资源利用与保护进行临界分析,可以较好的反映湿地利用的临界状态;采用该方法,七里海湿地耕地利用的年净收益为9 5941.42元/hm2,净损耗为18 072.75元/hm2,临界效益(△B)值为77 868.67元/hm2;养殖河蟹的年净效益为21 622.68元/hm2,净损耗为2 0274元/hm2,△B值为1 348.68元/hm2,说明在目前的社会经济发展水平下,耕地和养殖河蟹两种利用方式尚未超出开发利用的临界准则,七里海湿地仍然具有开发潜力。     

生态系统服务社会价值与生态价值的权衡与协同关系——以普达措国家公园为例

以香格里拉普达措国家公园为研究区,借助SolVES模型和InVEST模型,分别度量其社会价值（美学价值、文化价值、游憩价值）和生态价值（生境质量、碳储量、水源供给）的空间特征,并运用双变量空间自相关分析对二者空间权衡与协同关系进行研究。研究表明：① 社会价值的高值区呈“多核心,多条状”的空间格局,社会价值指数高达8.6（该指数介于1~10）,且距水体的距离越近对社会价值的贡献越大（贡献度为45.9%）;② 生态价值良好及优的空间范围占园区面积的1/2（49.91%）,主要位于原始森林保存良好的碧塔海片区和尼汝东北部扎诺一带;③ 社会价值与生态价值之间存在显著的空间依赖性,其中社会价值低,生态价值高的区域是园区最主要的空间聚集特征。该研究可为生态系统服务的可持续管理决策提供科学依据,以及有助于完善基于生态系统服务的社会?生态系统分析理论框架。